SHORT MEMOIRS ON METEOROLOGICAL SUBJECTS. 



395 



diminish the atmospheric pressure. But when now we see that the 

 pressure in the center of a whirl sinks very low so soon as these rains 

 fall in consequence of a rotatory motion of the air, must we then not 

 conclude, not that the rain, but more probably the whirl itself, is the 

 cause of the barometric depression, especially as mechanical principles 

 teach us that in the midst of a rotating mass of air the pressure must 

 decrease toward the axis of rotation f I therefore believe that in the 

 present state of our knowledge of the phenomena of storms we must 

 seek to explain the barometric minima of the storm centers by dynami- 

 cal laws. A step in this direction has been made by Ferrel (see "Silli- 

 man's Journal," January, 18G1 ; and " Nature," July, 1871).* I will re- 

 nounce this view whenever any one shall have completely demolished 

 the objections that can be raised against the origin of barometric minima 

 in consequence of an ascending air-current without rotatory motion. 



I have acknowledged that I have, in fact, expressed myself too gen- 

 erally in reference to an observation that one can with us note at any 

 time, and Ho£fmeyer remarks that in Denmark also the heaviest rains 

 mostly occur during the lowest pressures. Of course, however, this does 

 not prove that the rain must be the cause of the low pressure. This, and 

 the justification of my statement, at least for all places that are pro- 

 tected from the south and southwest winds, will be shown by the follow- 

 ing collation of the results of observations. 



Wind-roses for Barometric Pressure and Percentages of Rainfall. 



E .. 

 SB. 

 S... 

 SW 

 W.. 

 KW 

 if.. 



Bainfall. 



4 



2 



9 

 10 

 23 

 27 

 20 



4 

 3 



4 

 12 

 20 

 19 

 23 

 15 



Barom. 



755.1 

 751.7 

 750.0 

 749.7 

 749.5 

 751.7 

 752.8 

 754.7 



Number of years of obssrvation. 

 11 11 13 I 6 I 5 I 13 



Kain. 



Barom. 



746.6 

 745.0 

 744.2 

 742.5 

 741.3 

 743. 9 

 744.8 

 74G. 7 



Eainfall. 



5 



3 



7 



17 



29 



19 



14 



6 



Barometer. 



759.3 



758. 8 

 754.7 

 751.3 

 752.6 

 756. 

 757. 6 

 75a 7 



763.0 

 760.9 

 760. I 

 757. 3 

 757.3 

 759.0 

 760.8 

 762.8 



763.2 

 762.3 

 760.0 

 757.9 

 758. 5 

 760. 

 761.3 

 762.8 



On the lee side of the Alps (as at Vienna) and of the Eiesengebirge 

 [= Giant Mountains between Bohemia and Prussian Silesia] (as at Bres- 

 lau, Zechen, and Gorlitz), the greatest precipitation occurs with W. and 

 NW. winds, but on the North German slope with SW. winds. Even here, 

 however, the lowest pressure does not perfectly coincide with the max- 



[*NoTE BY THE TRANSLATOR.— Mr. Ferrcl's first memoir, Nashville Journal of Medi- 

 cine and Surgery, xi, 1856, and his elegant mathematical paper published in The 

 Mathematical Monthly, 1859 and 1860, vols, ii and iii, appear not to have been accessi- 

 ble to Professor Hauu.] 



